There has been widely used a display device, such as a liquid crystal display device or an organic EL display device, that includes pixels having thin film transistors.
Patent Literature 1 discloses a thin film transistor having a back-gate electrode formed under a semiconductor layer and a front-gate electrode formed over the semiconductor layer. Patent Literature 2 discloses a thin film transistor having a gate electrode formed above a semiconductor thin film and a back-gate electrode formed below the semiconductor thin film.